On 25/05/12 12:20, Henrique de Moraes Holschuh wrote: > On Fri, 25 May 2012, Salvo Tomaselli wrote: >>> Because paging out a couple Gigabytes is veeeeeery different from >>> writing a couple Gigabytes to disk, of course. >> >> Yes because writing that on disk will only block the thread performing the >> write, not every thread that tries to allocate memory. > > What IO scheduler are you using? It must not be CFQ. CFQ will happly > screw it up and stall both readers and writers when the number of dirty > pages gets too large (which will happen if you write a gigabyte file to > disk). > > Either that, or you're cheating and your backend devices are simply "fast > enough" that it doesn't matter (fast RAID or fast SSD). > > The real question is: what does it better under CFQ+IO contention? > Several threads doing filesystem IO, or the swapper? Hint: it is not an > easy question to answer because it depends on the load, type of load, > and backend device. > I think that any user that has been using Linux for a while knows how ugly the things become when the systems starts swapping. When the system is swapping, the whole system will become so unresponsive while the swapping process is taking place that even your mouse pointer will stop moving. And this is *very* *very* annoying. This is so annoying, that I even had configured my laptop with a very low amount of swap, since I rather prefer the oom-killer to kill the application that is filling the ram than rather suffer this annoying situation. So please, don't argue about theoretical things about virtual memory or IO schedulers. If you are a desktop Linux user, you should know how ugly the things get when the system is swapping. I don't know the ultimate reason behind this ugly behaviour of Linux when the swapping process is happening, but I know this is real and it happens because I have experimented this situation myself more than a couple of times. Regards! -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Carlos Alberto Lopez Perez http://neutrino.es Igalia - Free Software Engineering http://www.igalia.com ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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